The electrochemical behaviour of mild steel in phosphate-borate-sulphide solutions

The localized corrosion of mild steel in neutral buffered solutions containing sodium sulphide is studied using potentiostatic and potentiodynamic techniques complemented by scanning electron microscopy and energy dispersive X-ray analysis. The breakdown potential depends linearly with the logarithm of the sodium sulphide concentration. At potentials close to ? 0.70 V (SCE), the nucleation and growth of a ferrous sulphide layer replacing the initial ferrous hydroxide film occurs prior to pit growth. In the ? 0.70 to ? 0.60 V range the logarithm of the induction time for pit initiation decreases linearly with the reciprocal of the applied potential. At potentials more positive than ? 0.60 V the oxide formation hinders pit growth leading to a partial passivation. The results suggest that two-dimensional salt islands are formed before pitting as it has been postulated for iron in halide-containing solutions.     

Impact of transient chemistry on the corrosion potential of a steam turbine disc steel

The adoption of two-shifting in coal-fired power generation (switching from on-load to off-load conditions on a daily basis and off-load for the weekend) results in regular cycling of the solution chemistry of the condensed steam on the turbine discs. A first stage investigation has been made of the effect of such chemistry cycling on the corrosion potential of the disc steel. The corrosion potential is typically about +0.05 V (SCE) in off-load chemistry (aerated pure water) and below −0.6 V (SCE) in on-load chemistry (deaerated solution containing chloride or chloride and sulphate anions). The critical observation was the sluggish response of the corrosion potential upon restoration of deaerated on-load conditions with the implication of a likely increase in pit and stress corrosion crack development.     

Passivity breakdown of high purity iron and AISI 4340 steel in 0.5M NaCl solution

The anodic and cathodic electrochemical behaviour of high purity iron and of AISI 4340 high strength steel in unbuffered 0·5M NaCl solution has been studied. The results were correlated with the SCC failure mechanism of the steel. The pitting potentials of both high purity iron and AISI 4340 steel are coincident. Heat treatment affected the pitting potential of the steel very little. Failure of AISI 4340 steel under both anodic and cathodic polarization was found. SCC under anodic polarization was closely related to the pitting potential. Conditions at the metal-solution interface for pit maintenance are given.     

碳钢在人造小孔中阳极溶解的研究

<正> 孔蚀的发生与发展既受材料因素的制约,又受环境条件的影响。由于小孔在生长过程中其总表面积一直在变化,直接测定小孔生长速度十分困难,因此有人采用人工小孔模型以研究小孔的生长规律。本工作采用人造小孔模型系统研究了环境因素对碳钢单蚀孔阳极溶解的影响规律及蚀孔内表面膜的组成与作用。     

Electrochemical behavior of chalcopyrite in presence of Thiobacillus ferrooxidans

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Initial stage of localized corrosion in artificial pits formed with photon rupture on Zn-5 mass% Al alloy-coated steel

The photon rupture method, by which oxide film and metal are removed by focused pulsed Nd-YAG laser beam irradiation, was applied to form artificial micro-pits in Zn-5 mass% Al alloy-coated steel. The zinc alloy-coated layer was removed by pulsed laser irradiation treatment for about one second in a neutral buffer solution with NaCl. The rest potential transient with the laser treatment was measured. In the early stage of the laser treatment the rest potential of zinc alloy-coated steel changed to the negative direction immediately after every irradiation of a laser pulse and then returned to the previous value. However, after the steel substrate was exposed to the solution, the rest potential moved to the positive direction immediately after every irradiation of a laser pulse and then returned to the previous value. The amplitude and duration of the potential change after the laser irradiation increased with repetition of laser irradiation, related to the pit depth and the exposed area ratio of coated layer/steel substrate. The rest potential fluctuation difference can be explained by galvanic reaction change in the artificial pit formed by laser irradiation on the Zn alloy-coated steel.     

Eine Charakterisierung Der Lochfraßkorrosion Des Nickels-II. Wachstumskinetik Und Lochmorphologie In Neutralen Sulfat- Und Perchloratlösungen

Potentiostatic current-time-measurements in sulphate and perchlorate solutions result in a quadratic time dependence for the growth of single pits on high purity nickel. In connection with studies of the pit morphology a new model for the propagation of pits is suggested. According to this model the development of a pit depends on the formation of a hydroxide or oxide layer at the opening of the pit or within the pit area. The model permits a new interpretation of the critical pitting potential and its observed pH-dependence. Furthermore, it gives a qualitative explanation of the influence of solution agitation on pitting corrosion.     

镁锂合金表面两步法化学镀镍工艺

首先,将预处理后的合金样品在碱式碳酸镍溶液中进行预镀,目的是在镁锂合金表面形成一层Ni-P合金薄膜;然后,在硫酸镍溶液中进行二次镀覆,获得具有保护作用的镀层。对获得的镀层的表面形貌、结构和抗腐蚀能力进行研究。结果表明：采用该方法能够在镁锂合金表面形成平整、光亮、致密的镀层,镀层与基体结合良好。镀层中磷含量达到13.56%（质量分数）,镀层的维氏硬度约为HV549。极化曲线测试表明,Ni-P镀层的腐蚀电位升高至-0.249V（vsSCE）,并有一个很宽的钝化区,这种现象显示该镀层具有良好的抗腐蚀能力。     

锰铜合金腐蚀裂缝在3.5%NaCl中的电化学行为

<正> 锰铜系高阻尼合金在铸态下具有优良的机械性能与阻尼性能,是一种新的舰艇螺旋浆材料。该合金的主要成份是:35～36%Cu,4～4.5%Al,2.5～3.5%Fe,1～2%Ni,余量 Mn,实艇试验表明,采用这种合金对降低螺旋浆的振动和噪声有明显的效果。但是,锰铜合金在海水介质中有 SCC 敏感性。实验室试验得出,该合金在3.5%NaCl 中的 K_(?)cc 约等于26kgf/mm~3 /2。现场试验也发现,经焊补的锰铜合金螺旋浆很快在焊缝周围出现开裂。本工作沿用前人的方法,采用闭塞电池模拟腐蚀裂缝,初步探讨了锰铜合金在海水介质中发生 SCC 的原因及可能防止的方法。     

Characterisation of calcareous deposits on freely corroding low carbon steel in artificial sea water

Abstract

Calcareous deposits were formed on steel under cathodic protection conditions in artificial sea water at various potentials from ?0·900 to ?1·400 V(SCE). The deposition calcareous layers were characterised by electrochemical impedance spectroscopies, scanning electron microscopy observations and X-ray diffraction analyses. At 20°C, the deposits were composed of calcite CaCO₃ when formed at various potentials in solution 1, of brucite Mg(OH)₂ and aragonite CaCO₃ when formed at potentials from ?0·900 to ?1·200 V(SCE) and only of brucite when formed at potentials E??1·300 V(SCE) in solution 2. Magnesium seems to influence the corrosion behaviour of freely corroding steel by causing calcium carbonate to precipitate as aragonite. Aragonite is more effective in covering the surface than calcite and is therefore more functional in preventing oxygen from reaching the steel surface, thereby lowering the corrosion rate.     

Effect of Sulphur and Manganese on Nucleation of Corrosion Pits in Iron

Abstract

A study has been made of the effect of sulphur and manganese concentrations in iron on its tendency to pitting in a buffered potassium chloride solution. As revealed by electron microprobe and microscopic examinations, (Mn, Fe)S_x inclusions are the main sources of pit nucleation. Corrosion most frequently starts within the boundary region between the inclusion and the passive metal. Electrochemical investigations have shown that the critical pitting potential of the alloys under investigation, irrespective of S content, is lower than the corresponding value for ultra-pure iron. Mn has a dual effect on fhe resistance of Fe to pitting: it slightly increases the critical pitting potential, but it forms the sulphide inclusions at which the pits nucleate.     

XPS研究Ti32Mo在浓盐酸溶液中钝化膜结构

用XPS研究了Ti32Mo在70℃、4 mol/L盐酸溶液阳极电 位为02 V和09 V时的钝化膜结构和组成.结果表明，钝化膜是由表层和过渡层组成的双层结构.对于阳极电位为02 V的试样，钝化膜富集因子f(Mo)随溅射深度增加，由最外层的175变化到8 nm时的140；而对于阳极电位为09 V的试样，钝化膜富集因子f(Mo)在132～142之间变化.钝化膜的表层可成Ⅰ和Ⅱ两个亚层，其组成主要是Ti和Mo不同价态的氧化物、氢氧化物和氯化物.     

Corrosion of Zinc and Steel in Dilute Aqueous Solutions

Abstract

Because of the wide use of galvanised steel pipes for conveying a variety of aqueous solutions a study has been made of the effects of the presence of chloride, nitrate and carbonate-bicarbonate ions on the relative potentials of zinc and steel. In the majority of solutions used, the potential of steel fell to an approximately steady value between ?550 and ?700 m V SCE, presumably due to anodic depolarisation. However, the behaviour of the zinc potential was irregular and depended on the type of solution employed. In particular, chloride ions were found to reduce the tendency towards ennoblement while the presence of nitrate and carbonate-bicarbonate ions raised the zinc potential sufficiently to produce a reversal of the potential of the zinc-steel couple.     

Influence of electrodeposition potential,TiO2 nanoparticles and chromium (III) inhibitor addition on the corrosion protection performance of organosilane coating on aluminium

In this work, the anticorrosion properties of phenyl trimethoxysilane (PTMS) films coated on aluminium 5000 series alloys were studied. PTMS films were deposited at various cathodic potentials. The optimum electrodeposition potential was found to be ?0.8?V vs. SCE. The coatings were also modified by different amounts of nano-TiO₂. In order to introduce corrosion inhibition and a self-repair property of the PTMS film, the addition of chromium (III) corrosion inhibitor in the presence of nano-TiO₂ was studied. The anticorrosion performance of coatings was investigated in a 3.5 wt.% NaCl solution. At optimum deposition potential, the ‘critical’ nano-TiO₂ and Cr(III) contents were both observed, under which the obtained PTMS coatings show the highest anticorrosion performance. The surface morphologies of PTMS coatings were examined by scanning electron microscopy. The results showed that the coatings deposited at ?0.8?V vs. SCE, from 20?ppm of nano-TiO₂ and 0.003 M Cr(III) inhibitor present uniform and compact morphologies.     

Corrosion behavior of Cu–Al–Be shape memory alloys with different compositions and microstructures

The corrosion behavior of Cu–Al–Be shape memory alloys with different microstructures and Be content in a 3.5% NaCl solution was studied by weight loss, cyclic anodic polarization and chronoamperometric measurements. The beryllium has a beneficial effect in β alloys. A pitting potential of −100 mV/SCE was found by anodic polarization tests for all the studied alloys, corresponding to the formation of pits produced by severe dealuminization. Samples with precipitates were more susceptible to pit formation. The corrosion behavior is strongly affected by the alloy microstructural conditions, and the β samples present higher pitting resistance and repassivation ability.     

Effect of halide ions on the nucleation of corrosion pits in iron

The kinetics of the pit nucleation in iron in borate buffer solution containing bromides and iodides (0.01 n–0.5 n) has been investigated, and the results have been compared with those obtained for chloride solutions. It has been found that the critical pitting potential, E_cp, decreases linearly with the logarithm of the halide concentration. At constant potential, E, the logarithm of the induction period of pit nucleation decreases linearly with the reciprocal of the potential difference ΔE = E-E_cp. The mechanism of the aggressive action of the halide ions on the passive film is discussed.     

A537钢及工业纯铁在3.5%NaCl水溶液中腐蚀疲劳裂纹扩展机理的识别

本文根据外加电位对腐蚀疲劳裂纹扩展速率的影响,断口微观形貌特征及声发射活动性分析三种判别方法,研究了A537钢及工业纯铁在3.5%NaCl中性水溶液中腐蚀疲劳裂纹扩展机理。结果表明,扩展机理取决于外加电位值。对A537钢,外加电位在-800mV(SCE)以上时,裂纹扩展以阳极溶解控制为主,以下时以氢脆控制为主。对工业纯铁,对应的转换电位为-1000mV(SCE)。     

A study of electrical chloride extraction of iron artifacts

The chloride extraction rule of iron artifacts was studied by electrical methods. The effect of the current and potential value on the desalination result of simulated iron artifacts was studied through the galvanostatic and potentiostatic experiments; the ingredients of the rust before and after treatments were also analyzed by the X‐ray diffraction (XRD). It has been found that the optimal current density was between ?0.50 and ?0.75 mA/cm² and the optimal potential was between ?1.175 and ?1.200 V. The phase of the samples rusts transformed after treatment, as well as the anti‐corrosion performance improved.     

Metastable pitting behavior of aluminum single crystals

The metastable pitting behavior of aluminum single crystals (99.999% pure) with orientations of (100), (110) and (111) was followed as a function of potential at potentials below the pitting potential in a deoxygenated 0.6 M NaCl solution. The (111) crystal face exhibited the highest number of metastable events at a given potential. The (100) face showed the second highest number of events, while the (110) had the least number of events. The peak pit currents for the three surfaces were not statistically different in the potential region −0.785 to −0.745 V vs. SCE indicating that the amount of electrochemical charge passed in a breakdown event is independent of orientation. These results are discussed in relation to the nature of the oxide film and the atomic planar densities of the three orientations.     

Initiation and propagation of stainless steel pitting corrosion under heat flux

An effect of heat flux on initiation and propagation of pitting corrosion of austenitic stainless steel in chloride environment has been studied using electrochemical and exposure methods. The experiments were performed at constant surface temperature of 60°C and heat flux from ? 15 to + 74 kW m^?2. The presence of heat flux from metal to solution shifted the breakdown potential towards noble values and lowered the pit density, whereas the pit propagation rate increased. Presence of maximum heat flux caused, in comparison with isothermal conditions, increase of the breakdown potential by approx. 100 mV, reduction of pit density by 30% and increase of the average pit depth by 40%. The positive effect of heat flux from metal to solution was given mainly by improving the protective ability of the passive film, as the amount of oxygen available at the metal surface increased. With a smaller significance, the effect of intensified mass transfer, which made accumulation of the chloride ions on the surface more difficult, occurred.